Electrical fuse and heater units

ABSTRACT

An electrical fuse unit is shown to comprise a composite material embodying a layer of resilient metal sheet material, an electrically insulating sheet material arranged substantially coextensive with and bonded to a sheet surface of the metal sheet material, and at least one electrically conductive fuse element of selected thickness bonded to the insulating sheet material, the fuse element having a pair of terminal portions of selected width electrically interconnected by an intermediate fuse portion of relatively smaller width which is fusible in response to the passage of selected electrical current through the fusible portion. The composite material has a portion formed into semicylindrical shape and has parts of the terminal portions of the fuse element disposed on opposite sides of the semicylindrical portion of the composite material. In this arrangement, the fuse unit is adapted to be disposed between a pair of electrical contact means for resiliently engaging the fuse terminal portions with respective contact means.

[ 72] Inventors Ashok R. Hlngorany;

Joseph A. Wllloughby, both of, 34 Forest St., Attleboro, Mass. 0270: 21 Appl.No. 843,690 [221 Filed My, 1969 [45] Patented June 15,1971

[54] ELECTRICAL FUSE AND HEATER UNITS 5 Claims, 14 Drawing Figs.

Primary Examiner-Bernard A. Gilheany Assistant ExaminerDewitt M. Morgan Attorneys-Harold Levine, Edward J. Connors, Jr., John A.

Haug, James P. McAndrews and Gerald B. Epstein ABSTRACT: An electrical fuse unit is shown to comprise a composite material embodying a layer of resilient metal sheet material, an electrically insulating sheet material arranged substantially coextensive with and bonded to a sheet surface of the metal sheet material, and at least one electrically conductive fuse element of selected thickness bonded to the insulating sheet material, the fuse element having a pair of terminal portions of selected width electrically interconnected by an intermediate fuse portion of relatively smaller width which is fusible in response to the passage of selected electrical current through the fusible portion. The composite material has a portion formed into semicylindrical shape and has parts of the terminal portions of the fuse element disposed on opposite sides of the semicylindrical portion of the composite material. In this arrangement, the fuse unit is adapted to be disposed between a pair of electrical contact means for resiliently engaging the fuse terminal portions with respective contact means.

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ELECTRICAL FUSE AND HEATER UNITS l-leretofore fuses have been variously complexly constructed, as for example with metallic terminal cups joined by a fragile fuse wire surrounded "by a protective glass sleeve carried by the cups. Circuitry without fuses or heaters has been constructed on what are called circuit boards made by printed and etched circuitry applied directly to insulating boards or ceramic platensJn. some cases an individual board of this type carried an individual fuse element (see U.S. Pat. No.

2,941,059). However, the insulating board form was subject to warping, abrasion and spontaneous disintegration, and the ceramic form was quite fragile. Neither of them could be bent to desired fuse or heater shapes. Moreover, none of these incorporating any fuselor heater elements provided any effective heat sink, as in many cases is desirable. In the case of heate'r constructions it has heretofore been costly and clumsy tions to locations having higher temperatures and/or corrosive ambient conditions. Heaters may be more closely organized with heating panels, thermostatic composites or the like which they serve. Expended fuses or damaged heaters are more apparent visually. The units are very compatible with electrical systems employing conventional printed circuit boards. Other objects and features will be in part apparent and in part pointed out hereinafter.

Referring to the accompanying drawings:

FIG. 1 illustrates one-form of a fusemade according to the invention;

FIG. 1A on a reduces scale illustrates how a unit such as shown in FIG. 1 is made;

FIG. 2 illustrates a bent variation of the FIG. 1 form;

FIG. 3 is a plan view of a multiple twin fuse unit made according to the invention, a small portion of certain layers being broken away;

FIG. 4 is a plan view of a line terminal block for accepting the unit of FIG. 3, as shown by the broken dart;

FIG. 5 is an enlarged cross section taken on line 5-5of FIG. 4 and illustrates one of the line terminal clips in the terminal block;

FIG. 6 is a plan view of a quadrated form of a multiple fuse unit; 1

FIG. 7 is a view like FIG. 6 illustrating a modification of the quadrated form of unit;

FIG. 8 is an illustration showing another form of an individual fuse;

FIG. 9 is anend view partly in section showing the application of the FIG. 8 form of the invention to line terminal clips;

FIG. 10 illustrates modified fuse terminals of a multiple fuse unit;

FIG. 11 is a view, partly in section, showing line terminal clips for the reception of the fuse terminals illustrated in FIG. 10;

FIG. 12 is a plan view of a heater unit incorporating a thermostat as a backing layer; and

FIG. 13 is an enlarged cross section taken on line 13-13 of FIG. 12.

Corresponding reference characters indicate corresponding parts throughout the several views of the drawings. The drawings are not to a proportional scale, the thicknesses of various layers having been exaggerated for clarity.

Referring to FIG. I, numeral 1 indicates a metal backing layer which forms a sufficiently stiff support for normal handling of the finished fuse in placing it in, and removing it from,

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circuitry. However, under sufficient force-applied during manufacture it is bendable during manufacture as illustratedin FIG. 2. It may be single-ply or multiply. Any appropriate metal maybe employed such as, for example, steel, copper, or aluminum if atmospheric corrosion is to be resisted. In cases requiring it the back layer is made thick enough to constitute a good heat sink. Appropriate thicknesses for the backing layer are 'in the range of 20 to 50 mils, with about 25 mils preferred. The greater thicknesses are appropriate in those cases in which the backing layer is to function as a heat sink.

Attached to one face of the metal back is an etch-resistant insulating layer 3 composed of a polymer. The polymer material may be Teflon-coated Kapton. Teflon is a fluorocar bon and Kapton is a polyimide, both being trade names ofthe E. I. duPont de Nemours 8L Co. The Teflon forms a'good bond under heat and pressure. Mylar may be also used but requires attachment by one of the usual adhesives for such purposes. Mylar is also a duPont trade name. Kapton may also be used without the Teflon and attached by means of a similar adhesive. Ari appropriate range of thicknesses for the insulating layer 3 is 2 to 6 mils with about 2 mils preferred.

On the polymer layer 3 is a flat fuse element consisting of a calibrated link part 5 having terminal portions 7. The metal composing the fuse element is any of those well-known for the purpose, including zinc, copper, alloys such as those composed of bismuth, lead and tin, etc, The fuse element is what is left after a layer of conductive material attached to the top of the polymer layer 3has been etched away, as will appear. Appropriate thicknesses are in the range of 2 to 12 mils with 3 mils preferred. The shape of the fuse may be varied as desired, for example to include an shunt portion.

In FIG. 1A is illustrated a rapid method by which fuses made according to the invention may be constructed. This FIG. shows a sheet in strip form of starting backing material 1M from which backings such as l are made. To this strip is bonded in the manner above described a sheet in strip form 3M which provides the starting material to form insulation such as 3. To the strip SM is bonded, by plating or in strip form, fuse material 5M which provides the starting material from which fuse elements such as 5, 7 are obtained. It is to be understood that the term bonded layer for layer 5M includes a plated-on layerand a strip form of layer. The composite C is formed under heat and pressure, as required, by pressure rolling or in a platen type of press. The layered assembly 1M, 3M, 5M may be referred to in general as a starting composite.

The composite is converted to form fuse elements such as 5, 7 by printing etch-resist patterns on the conductive layer 5M by photographic, silk screen or other appropriate printing process. In the photographic process, by the development of the print formed in a photosensitive film on layer 5M, such a print is converted into insoluble etch-resist material. Unprinted portions being soluble are washed away. In the silkscreen process the print is applied directly in etch-resistant The dots D on the tab 7 in FIG. 1 indicate where circuitry may be attached by anyone of conventional means such as welding, soldering or any other appropriate means. It may be mentioned that when the layer 1 is made thick enough to act also as a heat sink to prevent overheating and change of calibration of the link portion 5, that this also prevents destruction of any soldered connections at D.

by curved end tabs 15. The tabs may be inserted in the usual printed and etched-out conductive fuse element 23. In this case the fuse element 23 extends peripherally around the cylindrical fonn. In FIG. 9 is shown how a fuse in FIG. 8 may be inserted between the springy line terminal clips 25 of a circuit 27. Numeral 26 is the insulating block which supports the clips.

Returning to FIG. 3, it illustrates a twin fonn of the invention in which a square, metal backing plate 29 shown at a broken-away portion carries the insulating polymer layer 31 upon which is the etched printed circuitry obtained as above described. In this case'the circuitry constitutes two separate but identical banks P, Q of circuit arrangements having l fuses each, numbered 33. From eachfuse are two leads extending to marginal terminal portions 35. Various groups of the fuses have common grounds as shown.

At numeral 37 is shown a line terminal block for 15 circuit lines 39 having 13 springy line terminal clips 41, as illustrated in FIGS. 4 and 5. The clips 41 are located on the bottom of a socket 42 in the tenninal block 37. The side of one-half of the composite fuse block as shown in FIG. 3 is inserted into the terminal block 37 as shown in FIG. 4. The terminals 35 engage the line terminal clips 41 respectively, which places the lower half of the fuse block into circuit. At this time the upper half of the block extends above the terminal block 37 and acts as a dead standby. If and when one of the fuses 33 blows, the user may extract the fuse block from the terminal block 37, turn it over and insert the inverted upper half into block 37. This restores all of the circuits. If desired a layer such as 31 with circuitry 33 and 35 thereon may be carried on the other side of the backing plate 29 to supply additional replacement circuits.

While it might appear that it would be wasteful to remove good unblown fuses from circuitry just because one, or less than all, has blown, this is not the case because of the economical construction, both in materials used and the manufacturing cost.

In FIG. 6 is shown in plan view a square multiple fuse block made in the manner which will be readily understood from the above descriptions. In this case the independent fused circuitries are quadrupled and placed in quadrature, as shown. Thus the FIG. 6 block numbered 43 has four quadrants 45 each of which carries three etched patterns forming three fuses 47 with their leads 49 extending to marginal tab portions 51. If the current and voltage in any two adjacent circuits are such as might cause leakage of current and/or heat between them across the insulating layer 46, then the block 43 may be punched out as illustrated at numerals 53. The form of the multiple fuse blocks shown in FIG. 6 may be used in connection with a suitable terminal block to make four fuse replacements in a circuit.

In FIG. 7 is shown a form of the invention like that shown in FIG. 6, except that in this case holes such as 53 are omitted. In this form a second polymer insulating layer 55 is bonded on the upper surfaces of the polymer layer 46 and the fused circuits. This prevents electrical leakage or excessive communication of heat between any two circuits on the entire board.

In both the FIG. 6 and FIG. 7 forms the back surfaces may have circuitry repeated thereon, as above described in the case of FIG. 3. Also, in both of these FIG. 6 and 7 forms of the invention are shown a hole 57 through the device by means of which it may be anchored by a suitable bolt or the like when in position in a terminal block. This prevents vibration or the like from ejecting the device from the terminal block.

In FIG. 10 is shown a form of the invention in which material layers 61, 63 and 65 generally correspond to the material layers 9, 11 and 13 of the unit illustrated in FIG. 2. In this form of the invention, the printed circuit elements (the fusible portions of which are not shown) are extended as tabs 69 on springy U-shaped meta] fingers 59. Extensions 67 of the insulating layer on fingers 59 underlie the tabs 69. vDimples 71 are 7 provided on both sides of the U-shaped fingers for detent action with spring receptor portions 73 of spring terminal clips 75, as illustrated in FIG. 11. Each clip 75 terminates a portion of a conductive circuit 76, further description of which is unnecessary in view of what has been said above. The parts of conductors 75 and 76 are molded into an insulating terminal I block 79. Connections are made by inserting the assembly shown in FIG. 10 into the assembly shown in FIG. 11.

The invention is not limited to the production of fuses. It

may also be used to form heater units as shown in FIGS. 12 and 13. In the example shown the backing plate 81 is composed of an assembly of bonded bimetal strips 83 and 85, on one side of which is carried a layer of insulating polymer layer 87 such as above described. On the polymer layer 87 is printed the circuitry 89 which is to form the heater for the thermostat. It has terminals 91 to which circuit connections may conveniently be made. In this case the material of which the etched circuitry made is chosen for its resistance characteristics for heating purposes such as Nichrome. It is often desirable that a bimetal thermostat be provided with a compactly arranged anticipating or like heater in close proximity thereto and the invention provides a simple low cost means for mounting the heater on the thermostat and in very close proximity thereto, for maximum rapid heat interchange entailing a minimum of losses.

It is to be understood that the backing plate 81 in FIG. 12 need not be a thermostatic bimetal strip but may be composed of a single metal, such as aluminum or two metals such as highly bent conductive and protective aluminum for layer and steel for the layer 83. In these cases the backing plate may function as a heating panel, thermostatic action being inconsequential if, as intended, the aluminum is thin and placed outside. It is further to be understood that a polymer layer may be applied to cover fuse or heater circuitry so that a unit would have a metal base, a polymer insulator thereon, a heater or fuse pattern on this polymer, and a protective polymer layer covering the heater or fuse pattern.

Highly accurate circuit values may be obtained, especially when a photographic process is used, because then the original art work for the required patterns may be made quite large. Any errors in such work are minimized by the photoreduction to the actual pattern size preceding etching. Thus the accuracy in the ultimate scale to which the fuses are made has been found to be on the order of about 10 times that of the master drawing accuracy.

The advantage of the metallic backing, when made thick enough to provide a heat sink, minimizes the deviation from the calibration of a fuse when operating under excessively high temperature. Heavy duty fuses will sometimes burn out under temporarily hot conditions when the current in the circuitry does not call for it. By the use of a thick enough metal backing as part of the fuse, heat may be abstracted from the printed circuitry to forestall this trouble. Fuses, and more particularly those for light duty and high accuracy of calibration and operating under conditions of ordinary temperatures, should in general be constructed with a backing layer such as 1 which will not supply much heat sink effect but only rigidity. Otherwise the heat sink effect may destroy the accuracy of calibration.

In view of the above, it will be seen that the several objects of the invention are achieved and other advantageous results attained.

As various changes could be made in the above constructions and methods without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense. i

We claim: 1 r 1. An electrical fuse unit comprising a composite material embodying a layer of resilient metal sheet material, an electrically insulating sheet material arranged substantially coextensive with and bonded to a sheet surface of said metal sheet material, and at least one electrically conductive fuse element of selected thickness bonded to said insulating sheet material,.

said fuse element having a pair of terminal portions of selected width electrically interconnected by an intermediate fuse portion of relatively smaller width fusible in response to the passage of selected electrical current therethrough, said composite material having a portion formed into semicylindrical shape and having parts of said terminal portions of said fuse element disposed on opposite sides of said semicylindrical portion of a cylinder greater than a semicylinder.

3. An electrical fuse unit as set forth in claim 1 wherein said composite material has two flat portions spaced form each 6 other and connected by said semicylindrical portion.

4. An electrical fuse unit as set forth in claim 1 having a plurality of said electrical fuse elements bonded to said insulating sheet material in spaced relation to each other.

5. An electrical fuse unit comprising a layer of resilient metal sheet material having a portion thereof formed into a plurality of U-shaped fingers each including a semicylindrical sheet metal portion spaced from the ends of said U-shaped fingers, an electrically insulating sheet material arranged substantially coextensive with and bonded to said metal sheet material, and a plurality of electrically conductive fuse elements of selected thickness bonded tosaid insulating sheet material extending along said respective fingers over said semicylindrical portions thereof, each of said fuse elements having a pair of terminal portions of selected'width electrically interconnected by an intermediate fuse portion of relatively smaller width fusible in response to passage of selected electrical current therethrough, each of said semicylindrical portions of said fingers of said metal sheet material being resiliently stressable by a pair of electrical contact means in resiliently engaging respective terminal portions of said fuse elements with said contact means. 

1. An electrical fuse unit comprising a composite material embodying a layer of resilient metal sheet material, an electrically insulating sheet material arranged substantially coextensive with and bonded to a sheet surface of said metal sheet material, and at least one electrically conductive fuse element of selected thickness bonded to said insulating sheet material, said fuse element having a pair of terminal portions of selected width electrically interconnected by an intermediate fuse portion of relatively smaller width fusible in response to the passage of selected electrical current therethrough, said composite material having a portion formed into semicylindrical shape and having parts of said terminal portions of said fuse element disposed on opposite sides of said semicylindrical portion of the composite material whereby said fuse unit can be disposed between a pair of electrical contact means for resiliently engaging said fuse terminal portions with said respective contact means.
 2. An electrical fuse unit as set forth in claim 1 wherein said composite material has a generally cylindrical shape forming a portion of a cylinder greater than a semicylinder.
 3. An electrical fuse unit as set forth in claim 1 wherein said composite material has two flat portions spaced form each other and connected by said semicylindrical portion.
 4. An electrical fuse unit as set forth in claim 1 having a plurality of said electrical fuse elements bonded to said insulating sheet material in spaced relation to each other.
 5. An electrical fuse unit comprising a layer of resilient metal sheet material having a portion thereof formed into a plurality of U-shaped fingers each including a semicylindrical sheet metal portion spaced from the ends of said U-shaped fingers, an electrically insulating sheet material arranged substantially coextensive with and bonded to said metal sheet material, and a plurality of electrically conductive fuse elements of selected thickness bonded to said insulating sheet material extending along said respective fingers over said semicylindrical portions thereof, each of said fuse elements having a pair of terminal portions of selected width electrically interconnected by an intermediate fuse portion of relatively smaller width fusible in response to passage of selected electrical current therethrough, each of said semicylindrical portions of said fingers of said metal sheet material being resiliently stressable by a pair of electrical contact means in resiliently engaging respective terminal portions of said fuse elements with said contact means. 